It is essential that the steam turbines of large generating stations be effectively lubricated. During the operation of the turbines a certain amount of the steam used to drive the turbines condenses either before or after it makes contact with the lubricating oil for the turbine. When new turbines are first put into operation, the volume of condensate becoming mixed with the lubricating oil normally is relatively small in most equipment. However, as the turbines age, wear gradually decreases the effectiveness of the seals separating the steam from the lubricating oil. This wear, however, is not enough to adversely affect the operating efficiency of the turbine. So long as the efficiency is not affected, the cost of replacing the worn seals is not justified. Further, tolerance variation within practical and acceptable limits can and does significantly affect the rate of steam leakage into the lubricating oil, even in new equipment. Further, even new equipment having the most effective seals will allow an unacceptable quantity of condensate to accumulate in the lubricating oil after a period of use.
The accumulation of this condensate creates a difficult and expensive problem. In the past, one method was simply to replace the oil. Since the volume of oil involved runs into thousands of gallons, this has become very expensive. Further, disposing of such oil has also become very expensive. Some processes have been developed for separating the condensate from the oil. These processes, however, have been slow and cumbersome and not adaptable to use at a generating plant. As a consequence, one of the more common procedures in use today is to replace the used oil with fresh, condensate free oil. The used oil is placed in tanks and shipped to a remote, central processing facility where it is purged of both the condensate and any accumulated particulate matter so it can be reused. Once again, while this procedure is less expensive than simply replacing the oil and disposing of it, it is expensive, labor intensive and cumbersome.
In an attempt to provide on site processing of the lubricating oil, centrifuges and vacuum dehydrators have been used. However, these units have inadequate capacity and further, at best, have been shown to be marginally capable of doing an efficient job. This invention, for the first time, makes it possible to process the lubricating oil at the generating station and return it to the system as a continuous closed circuit procedure incorporated into the lubrication system at a rate well in excess of the rate of ingression of the water contaminant.
The lubricating oil leaving the turbines contains three forms of water, which are free water, water in an oil emulsion and dissolved water. The dissolved water is not a problem to the turbine equipment and this invention does not deal with it. The invention removes all of the free water by gravity separation. The invention is directed to the removal of the water from the oil/water emulsion. This has never been done before at a rate and in a manner which is compatible with the oil usage rate of a major turbine generating facility. While the removal of water from an oil/water emulsion has long been known, the rate at which the process could be carried out was so slow that it has been of no practical value in dealing with the problems of a steam turbine generating station. For example, the known processes could not process the oil requirements of a large steam turbine unless the facility was so large as to be wholly impractical and, even then, would be incapable of the degree of dewatering achieved by this invention. Another parameter of the problem is temperature. Even though such units would work when the oil temperature was 120.degree. F. and the viscosity low, it was found that the coalescence process ceased when viscosity exceeded 100 ssu. Thus, prior art units using coalescence not only had unacceptably low flow capacity, they were completely inoperative at some normal operating temperatures and viscosities. It had long been recognized that whatever water separation system was to be used it should be capable of processing oil having a viscosity in excess of 200 ssu.